In an industrial gas turbine, shroud segments are fixed to turbine shell hooks in an annular array about the turbine rotor axis to form an annular shroud radially outwardly and adjacent the tips of buckets forming part of the turbine rotor. The inner wall of the shroud defines part of the gas path. Conventionally, the shroud segments are comprised of inner and outer shrouds provided with complimentary hooks and grooves adjacent their leading and trailing edges for joining the inner and outer shrouds to one another. The outer shroud is, in turn, secured to the turbine shell or casing hooks. In an exemplary configuration, each shroud segment has one outer shroud and two or three inner shrouds.
Two common approaches have been taken for the configuration of inner shrouds in the past; an opposite hook design and a C-clip design. The opposite hook design is the more traditional approach and incorporates oppositely projecting hooks on the leading and trailing edges that are retained by the outer shroud. The main service disadvantage with such an arrangement is that the inner shroud cannot be removed in the axial direction; it can only be slid out of the casing circumferentially. This access limitation requires any mating shroud assemblies to be removed before the shroud of interest can be accessed.
Thus, for the traditional opposite hook design, to remove a particular inner shroud, all preceding shrouds had to be removed by disengaging their anti-rotation pins and then sliding them out circumferentially, one-by-one, until the shroud of interest is accessible. For a 6C-engine part count of 66, this would require removing as many as 5 additional outer shrouds, along with 15 inner shrouds, before the inner shroud of interest is accessible.
The second conventional approach mentioned above, the C-clip design, provides a service enhancement to the opposite hook approach that allows axial access to the inner shroud. A conventional C-clip design is schematically illustrated in FIG. 1. As can be seen, like the traditional opposite hook approach, this arrangement also comprises leading and trailing edge hooks 10,12 projecting in opposite directions. However, the trailing edge hook 12 is retained with a separate C-clip 14, as opposed to being retained by the outer shroud 16. By removing the C-clip 14, the inner shroud 18 can be removed in the axial direction as shown by arrow A, thereby enhancing service access by allowing only the shroud 18 of interest to be removed. It should be noted, however, that at least one adjacent inner shroud, approximately one to three shrouds on each side (not shown), must still be shifted circumferentially to clear the cloth seals.
There are two main disadvantages of the above-described C-clip arrangement. The first is the added complexity of the additional C-clip components and features. These components and features include the C-clip itself, an anti-rotation pin, and the machined features required to accommodate axial and radial locating surfaces, a bearing surface for the C-clip, and the retention pin holes. A second disadvantage of the C-clip arrangement is that to allow service access to the C-clip pin, the stage two nozzles in the area of interest must be shifted circumferentially, which requires removal of the nozzle anti-rotation pins.
Thus, further service enhancements, such as improved service access and reduced complexity, would be desirable.
The present invention proposes to modify the stage one inner shroud to reverse the leading edge hooks as compared to the traditional opposite hook design and C-clip design to allow for axial removal of the shroud of interest without removal of additional shrouds. Providing a reverse hook arrangement in accordance with an embodiment of the invention simplifies access without the added complexity of the C-clip design.
Thus the invention may be embodied in a stator shroud segment comprising: an outer shroud having a, leading, upstream edge and a trailing, downstream edge, and radially inner and radially outer faces, said outer shroud comprising a leading edge hook and a trailing edge hook, both said hooks of said outer shroud projecting in a first, axial direction; a plurality of inner shrouds each having a leading, upstream edge and a trailing, downstream edge, and radially inner and radially outer faces, said inner shroud comprising a leading edge hook and a trailing edge hook, both said hooks of said inner shroud projecting in a second, axial direction, diametrically opposite said first axial direction; said leading and trailing hooks of each said inner shroud being respectively engaged with said leading and trailing hooks of said outer shroud, said engagement axially and radially locking said inner shroud to said outer shroud.
The invention may also be embodied in a stator shroud of a multi-stage gas turbine comprising: a shroud segment having a surface for, in part, defining the hot gas path through one stage and overlaying tips of buckets of said one stage forming part of a turbine rotor, said shroud segment having a leading, upstream edge and a trailing, downstream edge; said shroud segment comprising an outer shroud and at least one inner shroud connected thereto; said outer shroud having a groove defined adjacent and along each of said leading and trailing edges thereof, said grooves opening axially in a same direction; and said inner shroud having a leading edge axially projecting tab portion and a trailing edge axially projecting tab portion for respectively engaging said grooves of said outer shroud, said engagement axially and radially locking said inner shroud to said outer shroud
The invention may further be embodied in a method of disengaging and removing a first inner shroud having a leading edge hook and a trailing edge hook from an outer shroud having a leading edge groove and a trailing edge groove mutually engaged with said leading and trailing edge hooks of said first inner shroud, said leading and trailing edge hooks of said first inner shroud projecting in a same axial direction, said method comprising: one of removing and axially displacing a mating part on an upstream side of said first inner shroud; removing a first inner shroud anti-rotation pin engaging said first inner shroud and said outer shroud; removing anti-rotation pins from circumferentially adjacent inner shrouds and sliding said circumferentially adjacent inner shrouds until clear of cloth seals therebetween; sliding said first inner shroud axially to disengage the leading and trailing edge hooks from said leading and trailing edge hooks of said outer shroud; and displacing said first shroud radially to disengage and remove said first inner shroud.